DE10220555A1 - Method for operating a two-stroke engine and two-stroke engine - Google Patents

Abstract

A two - stroke engine (1) for a working device has a combustion chamber (3) formed in a cylinder (2) with a piston (5, 21) which, via a connecting rod (6), rotates a crankshaft (7) mounted in a crankcase (4) ) drives. The two-stroke engine (1) comprises at least three overflow channels (10, 11, 20) which connect the combustion chamber (3) to the crankcase (4) at predetermined control times. In the area of an overflow channel (10, 11, 20), fuel is injected at predetermined control times, a first partial amount of the fuel being injected into the channel synchronously with overflow and a second partial amount from a previous injection cycle from the crankcase (4) into the combustion chamber (3) transgresses. For this purpose, an injection nozzle (19) is arranged in at least one overflow channel (10), which injects fuel into the overflow channel (10) open to the cylinder (2).

Description

The invention relates to a method for operating a Two-stroke engine specified in the preamble of claim 1 Genus and a two-stroke engine to carry out the Method according to the preamble of claim 13 or the Claim 20.

A two-stroke engine is known from EP 0 302 045 B1, in which in the area of an overflow channel fuel into the combustion chamber is injected. To be one even at high speeds to ensure adequate fuel supply begins Injection before opening the overflow channel. There the overflow channel opens shortly after the injection, the amount of fuel injected completely into the combustion chamber entered. The crankcase must be lubricated separately.

The invention has for its object a method for Operation of a two-stroke engine to provide a separate Lubrication of the crankcase is unnecessary. Farther a two-stroke engine is to be specified with which the method can be carried out.

This task is accomplished by a process with the characteristics of Claim 1 and by a two-stroke engine with the features of claim 13 and with a two-stroke engine with the Features of claim 20 solved.

For the procedure for operating a two-stroke engine provided that predetermined in the area of an overflow channel Control times fuel is injected, at least in a speed range a first subset of the fuel, that gets into the combustion chamber for combustion, is injected overflow synchronously and a second subset at least one previous injection cycle from the Crankcase enters the combustion chamber. The fuel that passes from the crankcase into the combustion chamber, serves especially in combination with added oil, one sufficient crankcase lubrication. At the same time ensures that there is sufficient fuel in the Combustion chamber can get to the combustion chamber while the overflow channels are open so that the engine up to even at high speeds works smoothly at 15,000 revolutions / minute. Especially when idling and in the low partial load range, it can however, be advantageous that up to 100% of the fuel ins Crankcase is injected.

The fuel is expediently turned into the combustion chamber injected end of the overflow channel. This will good fuel delivery into the combustion chamber guaranteed. It is intended that the ratio of the two Partial quantities depend on each other depending on speed and / or load is adjusted. Thus, an optimal combustion in the Ensured combustion chamber and sufficient at the same time Crankcase lubrication can be achieved. Beginning will be advantageous and / or end of the injection load and / or adjusted depending on the speed. The injection always takes place overflow synchronous, d. i.e., in a period of time, in the crankcase and Combustion chamber fluidly with one another via the overflow channels are connected. The fuel is advantageous at one Crankshaft angle between 40 ° before UT and 70 ° after UT injected overflow synchronously. For good combustion and one sufficient crankcase lubrication is provided that at least in a speed range 15% to 90% of that for a Combustion required fuel quantity overflow synchronously be injected.

Fuel in the region of an outlet is advantageous Overflow channel injected. Expedient is given to Fuel timing injected into the crankcase. The fuel that accumulates in the crankcase is used Lubrication, with the fuel flowing through the inlet into the Crankcase flowing air forms a fuel / air mixture. The fuel / air mixture flows through the overflow channels in the combustion chamber. Thus it forms in the crankcase injected fuel is a subset of that for combustion Available fuel. This subset settles over several injection cycles into the crankcase injected fuel quantities together. The will be advantageous Fuel through a common injector both overflow synchronously in the overflow channel as well as in the crankcase injected. To provide the for combustion required fuel and for crankcase lubrication therefore only one injector is required. The is expedient Fuel injected into the crankcase at timing, in which the overflow channel to the combustion chamber through Piston shirt is closed. The piston is thus during the injection of fuel into the crankcase in the area top dead center. In particular, fuel is used in one Crankshaft angle between 100 ° before TDC and 50 ° after TDC ins Crankcase injected. The injection into the crankcase is therefore from the overflow synchronous injection in the Combustion chamber separated in time. Find each crankshaft revolution thus two injection cycles instead.

Has a two-stroke engine for performing the method at least three overflow channels. In at least one Overflow channel opens an injection nozzle, the overflow channel to Cylinder is open. The injector can thus vary Piston position overflow synchronously in the combustion chamber and in Top dead center area of the piston in the crankcase Inject fuel. The open towards the cylinder Overflow channels can be manufactured easily and inexpensively become. Separate lubrication devices or Mixture preparation devices are not required.

The injection nozzle is particularly in the area of the Combustion chamber facing end of the overflow channel arranged and on an electronic mixture dosing system connected. The electronic mixture dosing system enables an exact Control of the start and end of injection. The Injection times can depend on the engine speed and load be adjusted at short notice. Even with fast speed or Load changes will be a consistently cheap one Allows fuel supply. Low flushing losses reached when the injector is in an outlet Overflow channel opens.

An overflow channel remote from the outlet is expediently the outlet arranged opposite. However, it may be appropriate that a outlet overflow channel opposite the position in which the Middle plane divides the overflow channel symmetrically, in Cylinder circumferential direction is arranged offset. In particular are approximately two outlet near and two outlet overflow channels arranged symmetrically to the central plane. It can be convenient be an injection nozzle on each overflow channel remote from the outlet to arrange. This results in symmetrical relationships in the combustion chamber. By arranging only one injector one of the symmetrically arranged outlet However, an injection nozzle can be dispensed with overflow channels.

For another two-stroke engine to perform the The method provides that a Injector opens and a piston window is provided in the piston is the overflow channel with the crankcase in the area the top dead center of the piston fluidly connects. The Overflow channels are in one area with this two-stroke engine their longitudinal extent separated from the cylinder educated.

The piston window is expediently at top dead center of the piston in the area of the injection nozzle. The injector thus injects directly into the crankcase. Advantageously flows the injector into an overflow channel remote from the outlet, wherein the overflow channel remote from the outlet is arranged opposite the outlet can be or opposite the position in which the median plane divides the inlet window of the overflow channel symmetrically, in Cylinder circumferential direction can be arranged offset. In particular, there are two near the outlet and two near the outlet Overflow channels arranged symmetrically to the median plane.

In order to obtain a good washing result, it is provided that in at least one overflow channel opens an air channel. Good air pre-storage can be achieved in this way. The Air duct expediently opens in the area of an inlet window in particular via a valve in the overflow channel. Through the Mouth in the area of the inlet window can be almost complete flushing of the overflow channel with fresh air achieve.

Further features result from the description and the Drawing, in the embodiments of the invention are shown. Show it:

Fig. 1 is a schematic representation of a longitudinal section through a two-stroke engine,

Fig. 2 is a schematic representation of the arrangement of the transfer channels in a section along the line II-II in Fig. 1,

Fig. 3 is a perspective view of a cylinder in the direction from the crankcase to the combustion chamber,

Fig. 4 is a diagram related to the beginning and end of injection are presented to the crankshaft angle over the rotational speed,

Fig. 5 is a diagram in which the power supplied to the crankcase fuel subset is shown on the rotational speed,

Fig. 6 is a schematic longitudinal section through the cylinder of a two-stroke engine.

The two-stroke engine 1 shown in Fig. 1 comprises a cylinder 2 and a cylinder 2 formed in the combustion chamber 3. The combustion chamber 3 is delimited by an up and down piston 5 . The piston 5 drives a crankshaft 7 mounted in the crankcase 4 via a connecting rod 6 . The crankshaft 7 rotates in the direction of rotation 16 . The two-stroke engine 1 has an inlet 9 which supplies the crankcase 4 with largely fuel-free combustion air. The air is compressed in the crankcase during the downward stroke of the piston together with fuel in the crankcase 4 and in the piston position shown in FIG. 1 passes through the overflow channels 10 and 11 into the combustion chamber 3 . The overflow channels 10 and 11 are open towards the cylinder 2 . They are limited in predetermined piston positions towards the crankcase 3 by the piston skirt 32 . During the overflow of the fuel / air mixture, fuel is injected into at least one overflow channel, which enters the combustion chamber together with the fuel / air mixture and is compressed in the combustion chamber 3 during the subsequent upward movement of the piston 5 . The fuel / air mixture in the combustion chamber 3 is ignited by the spark plug 17 in the region of the top dead center of the piston. During the subsequent downward movement of the piston 5 , the exhaust gases leave the combustion chamber 3 through the outlet 8 , while at the same time fresh fuel / air mixture flows into the combustion chamber 3 .

The crankshaft angle α shown in FIG. 1, which denotes the angle between the center 33 of the lower connecting rod eye 34 and the longitudinal central axis 13 of the cylinder 2 , is used to identify the position of the piston. The crankshaft angle α is measured from the longitudinal central axis 13 in the direction of the direction of rotation 16 . At the top dead center OT of the piston 5 , the crankshaft angle α is 0 ° and at the bottom dead center UT of the piston 180 °. Crankshaft angles before UT are measured from bottom dead center against direction of rotation 16 and crankshaft angles after UT in direction of rotation 16 . The same applies to top dead center OT.

FIG. 2 schematically shows a section along the line II-II in FIG. 1. The inlet 9 into the crankcase 4 is located below the section plane and is therefore shown in broken lines. The cylinder 2 has two overflow channels 11 close to the outlet and two overflow channels 10 remote from the outlet. An injection nozzle 19 , which is connected to a valve 18 , opens into one of the overflow channels 10 remote from the outlet. The valve 18 is advantageously designed as an electronic mixture metering system. Outlet 8 and inlet 9 are divided approximately centrally from the central plane 12 . The injection nozzle 19 opens approximately parallel to the central plane 12 on the side of the overflow channel facing the inlet 9 into the overflow channel 10 remote from the outlet. The injection nozzle 19 advantageously opens into the overflow channel 10 in the area of the roof 14 shown in FIG. 1. The roof 14 of the overflow channel 10 and the roof 15 of the overflow channel 11 respectively designate the side of the overflow channel which, viewed in the direction of the longitudinal central axis 13 , delimits the combustion chamber 3 .

In Fig. 3 an embodiment of a two-stroke engine 1 is shown, wherein only the cylinder 2 is shown in perspective view. The cylinder 2 has an inlet 9 and an outlet 8 opposite this. Symmetrically with respect to the middle plane of the inlet 9 and outlet 8, there are two overflow channels 11 near the outlet and two overflow channels 10 remote from the outlet. Adjacent overflow channels 10 , 11 are each separated by a wall 35 , which extends in particular in the area of the combustion chamber between the overflow channels. The overflow channels 10 , 11 are open towards the cylinder 2 . An injection nozzle 19 , which is connected to an electronically controlled injection valve 18 , opens into an overflow channel 10 remote from the outlet in the area of the roof 14 . The injection nozzle 19 opens into the overflow channel 10 in the region of the passage of the overflow channel into the cylinder 2 . However, other positions of the injection nozzle 19 can also be expedient. In particular, this can be inclined at different angles with respect to the central plane 12 or the longitudinal central axis 13 of the cylinder 2 . It may also be expedient to arrange injection nozzles 19 symmetrically on both overflow channels 10 . Instead of the two symmetrically arranged overflow channels 10 remote from the outlet, it may be expedient to arrange an overflow channel 10 opposite the outlet 8 . However, it may also be expedient to arrange an overflow channel 10 remote from the outlet in the cylinder circumferential direction in relation to the position in which the overflow channel is divided symmetrically by the central plane 12 . It can also be expedient to provide a larger number of overflow channels.

The control of the injection nozzle 19 is illustrated in a diagram in FIG. 4. In the area of the bottom dead center, ie at a crankshaft angle α between about 40 ° before UT and about 70 ° after UT, the overflow channels 10 , 11 are open to the combustion chamber 3 . The überströmsynchron are open ie, during the transfer channels to the combustion chamber 3, injected fuel is completely introduced into the combustion chamber. 3 The beginning 24 and the end 25 of the overflow-synchronous injection are plotted in FIG. 4 over the speed n. The beginning 24 and end 25 of the overflow-synchronous injection are varied via the speed n, the injection advantageously being carried out as late as possible, so that the end 25 of the injection occurs approximately at the time when the overflow channels 10 , 11 close. The speed n is given in Fig. 4 in revolutions / minute and the crankshaft angle α in degrees. It is envisaged that at least in a speed range 15% to 90% of the amount of fuel required for combustion will be injected overflow synchronously. At idle and low partial load as well as at high engine speeds, it can be advantageous to inject up to 100% of the required amount of fuel into the crankcase.

In the area of the top dead center TDC of the piston 5 , ie approximately at a crankshaft angle α between 100 ° before TDC and 50 ° after TDC, the fuel quantity injected via the injection nozzle 19 reaches the crankcase 4 . The start 27 and the end 28 of the injection into the crankcase 4 are also plotted in FIG. 4 over the speed n. Beginning 27 and end 28 of the injection into the crankcase 4 are adjusted via the speed n and are expediently at a crankshaft angle α between 100 ° before TDC and 50 ° after TDC, in particular between 70 ° before TDC and 20 ° after TDC. The injector 19 injects two partial quantities of the fuel required for combustion during one revolution of the crankshaft 7 .

At low speeds, for example at about 4,000 to 5,000 revolutions / minute, it is advantageous to inject about 20% of the fuel quantity required for the combustion synchronously and approximately 80% of the required fuel quantity are injected directly into the crankcase. With increasing engine speed, the fuel quantity injected overflow synchronously increases and the amount of fuel injected into the crankcase decreases. At a speed n of approximately 9,000 revolutions / minute it is provided that approximately 85% of the required fuel quantity is injected synchronously with overflow and only approximately 15% is injected into the crankcase 4 . As the speed n increases further, the quantity of fuel injected overflow synchronously decreases again and the quantity of fuel injected into the crankcase increases, so that the partial quantities in the range of approximately 11,000 revolutions / minute each amount to approximately 50%. At maximum speed, up to 100% of the required amount of fuel can be injected into the crankcase.

The diagram shown in FIG. 4 shows the distribution of the fuel quantities in the case of a large quantity of air supplied to the crankcase 4 through the inlet 9 . The amount of air that enters the crankcase 4 through the inlet 9 is determined in particular by a throttle valve arranged upstream of the inlet 9 . In this case, Fig. 4 shows the situation when the throttle valve is fully open.

In FIG. 5, the subset of x, which is injected directly into the crankcase 4, plotted over the rotational speed n. Depending on the prevailing load, the subset x is determined according to one of the curves 37 , 38 , 39 or 40 . The curves 37 , 38 , 39 and 40 are examples of all curves possible from full load to idle. The arrow 36 indicates the direction of decreasing load. At lower loads, at the same speed n, the proportion x of the fuel quantity injected into the crankcase increases. As shown in FIG. 5, in the area of the low speeds, ie in particular when idling, the partial quantity x injected into the crankcase is large in all the curves shown and decreases with increasing speed up to the nominal speed at approximately 9,000 revolutions / minute. If the nominal speed is exceeded, the proportion x of the fuel quantity injected into the crankcase increases again. The proportion x is therefore the lowest at the nominal speed. The partial fuel quantities injected into the crankcase and synchronized with the overflow are expediently adjusted additionally or alternatively to the speed-dependent adaptation depending on the load.

In FIG. 6, a cylinder 2 is a two-stroke engine 1 shown schematically. A combustion chamber 3 is formed in the cylinder 2 and is adjoined by an opening 44 for a spark plug. The combustion chamber 3 is delimited from the crankcase 4 by a piston 21 which drives a crankshaft (not shown) about the crankshaft axis 43 via the connecting rod 6 . The crankcase 4 is connected to the combustion chamber 3 in two fixed positions of the piston 21 via two overflow channels 20 , which are expediently arranged remote from the outlet. The overflow channels 20 open into the cylinder 2 with inlet windows 23 . An injection nozzle 30 opens at one of the overflow channels 20 . The injection nozzle 30 opens into the overflow channel 20 approximately in the region of the inlet window 23 . The injection nozzle 30 is controlled via an injection valve 45 , which is expediently actuated electronically.

In the top dead center of the piston 21 shown in FIG. 6, the overflow channel 20 is connected to the crankcase 4 via a piston window 31 . The injection nozzle 30 actuated in the region of the top dead center of the piston 21 thus injects through the piston window 31 directly into the crankcase 4 . With the piston 21 arranged at the bottom dead center, the injection nozzle 30 injects into the combustion chamber 3 . This expediently takes place in synchronism with overflow, ie when the fuel / air mixture passes from the crankcase 4 into the combustion chamber 3 . Instead of the piston window, the piston can be shortened in the area of the inlet window of the overflow channel and thus allow fuel to be injected into the crankcase at top dead center. As shown in FIG. 6, two symmetrically arranged overflow channels 20 remote from the outlet can be provided. However, it may also be expedient to arrange only one overflow channel 20 remote from the outlet, approximately offset in relation to the outlet or from this position in the circumferential direction. The overflow channel (s) can be open towards the cylinder 2 .

For low flushing losses, it can be provided that an air duct opens into at least one overflow duct, which air largely precludes the fuel / air mixture with fuel-free air. This allows a good separation of the exhaust gases from the inflowing mixture. The air duct can, for example, open into at least one overflow duct in the region of an inlet window via a valve. It may be expedient that air is stored upstream only in the overflow channels 11 near the outlet. However, it can also be expedient to store air in all overflow channels. The air duct can open into the overflow duct, for example, via a valve.

Claims (29)

1. A method for operating a two-stroke engine ( 1 ), in particular for a hand-held, portable work tool such as a chain saw, a power grinder and the like., The two-stroke engine ( 1 ) having a combustion chamber ( 3 ) formed in a cylinder ( 2 ) by a rising and falling piston ( 5 , 21 ) is limited, and the piston ( 5 , 21 ) drives a crankshaft ( 7 ) rotatably mounted in a crankcase ( 4 ) via a connecting rod ( 6 ), with an exhaust gas from the combustion chamber ( 3 ) laxative outlet ( 8 ) and an inlet ( 9 ) approximately opposite the outlet ( 8 ), with a central plane ( 12 ) which divides the outlet ( 8 ) and inlet ( 9 ) approximately centrally and which divides the longitudinal central axis ( 13 ) of the cylinder ( 2 ), and with at least three overflow channels ( 10 , 11 , 20 ), which predefine the combustion chamber ( 3 ). Connect the control times to the crankcase ( 4 ), characterized in that fuel is injected in the area of an overflow channel ( 10 , 11 , 20 ) at predetermined control times, at least in a speed range a first subset of the fuel which is used for combustion in the combustion chamber ( 3 ) is entered, overflow-synchronously injected and a second partial quantity from at least one previous injection cycle is provided, the second partial quantity passing from the crankcase ( 4 ) into the combustion chamber ( 3 ). 2. The method according to claim 1, characterized in that the fuel in the overflow channel ( 10 , 11 , 20 ) in the region of the end ( 14 , 15 , 22 ) of the overflow channel ( 10 , 11 , 20 ) which the combustion chamber ( 3 ) is facing, is injected. 3. The method according to claim 1 or 2, characterized in that the ratio of the two Subsets to each other speed and / or is adjusted depending on the load. 4. The method according to any one of claims 1 to 3, characterized in that the beginning ( 24 , 27 ) of the injection is adjusted depending on the load and / or speed. 5. The method according to any one of claims 1 to 4, characterized in that the end ( 25 , 28 ) of the injection is adjusted depending on the load and / or speed. 6. The method according to any one of claims 1 to 5, characterized in that fuel at a Crankshaft angle (α) between 40 ° before UT and 70 ° after UT is injected overflow synchronously. 7. The method according to any one of claims 1 to 6, characterized in that 15% to 90% of that for a Combustion required fuel quantity overflow synchronously is injected. 8. The method according to any one of claims 1 to 7, characterized in that fuel is injected in the region of an overflow channel remote from the outlet ( 10 , 20 ). 9. The method according to any one of claims 1 to 8, characterized in that fuel is injected into the crankcase ( 4 ) at predetermined control times. 10. The method according to claim 9, characterized in that the fuel is injected through a common injection nozzle ( 19 , 30 ) both overflow synchronously and in the crankcase ( 4 ). 11. The method according to claim 9 or 10, characterized in that fuel is injected into the crankcase ( 4 ) at control times in which the overflow channel ( 10 , 20 ) to the combustion chamber ( 3 ) is closed off by the piston skirt ( 32 ). 12. The method according to any one of claims 9 to 11, characterized in that fuel is injected into the crankcase ( 4 ) at a crankshaft angle (α) between 100 ° before TDC and 50 ° after TDC. 13. Two-stroke engine, in particular for a hand-held, portable work tool such as a motor chain saw, a grinder or the like., With a combustion chamber ( 3 ) formed in a cylinder ( 2 ), which is delimited by an up and down piston ( 5 ), and the piston ( 5 ), via a connecting rod ( 6 ), drives a crankshaft ( 7 ) mounted in a crankcase ( 4 ), with an exhaust ( 8 ) leading away exhaust gases from the combustion chamber ( 3 ) and an inlet ( 8 ) approximately opposite the outlet ( 8 ) 9 ) and with a central plane ( 12 ) which divides the outlet ( 8 ) and inlet ( 9 ) approximately in the middle and which comprises the longitudinal central axis ( 13 ) of the cylinder ( 2 ), the crankcase ( 4 ) in predetermined piston positions via at least three overflow channels ( 10 , 11 ) is connected to the combustion chamber ( 3 ), characterized in that an injection nozzle ( 19 ) opens into at least one overflow channel ( 10 ), the overflow channel ( 10 ) opening towards the cylinder ( 2 ) is. 14. Two-stroke engine according to claim 13, characterized in that the injection nozzle ( 19 ) is arranged in the region of the end facing the combustion chamber ( 14 ) of the overflow channel ( 10 ). 15. Two-stroke engine according to claim 13 or 14, characterized in that the injection nozzle ( 19 ) is connected to an electronic mixture metering system. 16. Two-stroke engine according to one of claims 13 to 15, characterized in that the injection nozzle ( 19 ) opens into an overflow channel ( 10 ) remote from the outlet. 17. Two-stroke engine according to one of claims 13 to 16, characterized in that an overflow channel ( 10 ) remote from the outlet ( 8 ) is arranged opposite. 18. Two-stroke engine according to one of claims 13 to 16, characterized in that an outlet-remote overflow channel ( 10 ) relative to the position in which the central plane ( 12 ) symmetrically divides the overflow channel ( 10 ) is arranged offset in the cylinder circumferential direction. 19. Two-stroke engine according to one of claims 13 to 16, characterized in that two overflow channels ( 11 ) near the outlet and two overflow channels ( 10 ) remote from the outlet are arranged symmetrically to the central plane ( 12 ). 20. Two-stroke engine, in particular for a hand-held, portable implement such as a chain saw, a grinder or the like., With a combustion chamber ( 3 ) formed in a cylinder ( 2 ), which is delimited by an up and down piston ( 21 ), and the piston ( 21 ) drives, via a connecting rod ( 6 ), a crankshaft ( 7 ) mounted in a crankcase ( 4 ), with an exhaust ( 8 ) discharging exhaust gases from the combustion chamber ( 3 ) and an inlet ( 8 ) approximately opposite the outlet ( 8 ) 9 ) and with a central plane ( 12 ) which divides the outlet ( 8 ) and inlet ( 9 ) approximately in the middle and which comprises the longitudinal central axis ( 13 ) of the cylinder ( 2 ), the crankcase ( 4 ) in predetermined piston positions via at least three overflow channels ( 20 ) is connected to the combustion chamber ( 3 ) and wherein each overflow channel ( 20 ) opens into the combustion chamber ( 3 ) with an inlet window ( 23 ), characterized in that an inflow into an overflow channel ( 20 ) Ritzdüse ( 30 ) opens and a piston window ( 31 ) is provided in the piston ( 21 ), which fluidically connects the overflow channel ( 20 ) with the crankcase ( 4 ) in the region of the top dead center of the piston ( 21 ). 21. Two-stroke engine according to claim 20, characterized in that the piston window ( 31 ) is in the top dead center of the piston ( 21 ) in the region of the injection nozzle ( 30 ). 22. Two-stroke engine according to claim 20 or 21, characterized in that the injection nozzle ( 30 ) is arranged in the region of the inlet window ( 23 ). 23. Two-stroke engine according to one of claims 20 to 22, characterized in that the injection nozzle ( 30 ) opens into an overflow channel ( 20 ) remote from the outlet. 24. Two-stroke engine according to claim 23, characterized in that an overflow channel ( 20 ) remote from the outlet ( 8 ) is arranged opposite. 25. Two-stroke engine according to claim 23, characterized in that an outlet-remote overflow channel ( 20 ) relative to the position in which the central plane ( 12 ) symmetrically divides the inlet window ( 23 ) of the overflow channel ( 20 ) is arranged offset in the cylinder circumferential direction. 26. Two-stroke engine according to claim 23, characterized in that two outlet-near and two outlet-far overflow channels are arranged symmetrically to the central plane ( 12 ). 27. Two-stroke engine according to one of claims 20 to 26, characterized in that in at least one Overflow duct opens an air duct. 28. Two-stroke engine according to claim 27, characterized in that the air duct in the area of Inlet window opens into the overflow channel. 29. Two-stroke engine according to claim 27 or 28, characterized in that the air duct with the Overflow channel is connected via a valve.